1. Field of the Invention
The present invention relates to an image input processing apparatus and method in which light (image) from the subject containing a near infrared light component is imaged and the near infrared light component is separated from the image data of the obtained imaging signal.
2. Description of the Related Art
The human sensitivity to colors and brightness is characterized in that humans have the sensitivity in the visible light region. While defined variously, the visible light region is typically an electromagnetic wavelength region whose upper limit lies in the vicinity of 700 to 750 nm (for example, 780 nm) and whose lower limit is a little less than 400 nm (for example, 380 nm). An infrared region adjoining the visible light region is called a near infrared light region, which is an electromagnetic wavelength region from the lower limit of 700 to 800 nm to the upper limit of 1.5 to 3 μm (for example, 2.5 μm).
However, the human eye has hardly any sensitivity to the longer wavelength side of approximately 700 nm. In addition, since near infrared light has harmful effects such as degrading color reproducibility, an infrared intercepting filter (infrared cut filter) is typically provided in an optical part that controls light (image) from the subject in the image sensing device.
Since the image sensing device itself has sensitivity also to infrared light, in highly sensitive cameras for night photography or surveillance, light (image) of a wide band from visible light to infrared light is imaged.
Since the ratio of the infrared light being contained differs according to illumination (light source) such as a fluorescent light or an electric bulb and differs according to time even in the case of sunlight, whether to intercept infrared light or not is determined according to such a photographing environment change.
A technology is known in which to realize a camera that copes with any photographing environments to meet the above-described demand, visible light and infrared light are received by the same image sensing device by using a rotary type wavelength separating optical system as an input optical system (see, for example, JP-A-9-166493).
According to this technology, for example, switching between insertion and extraction of the infrared cut filter onto and from the incident optical path is made by a rotary mechanism or the like. When the infrared cut filter is inserted, a visible light color image not influenced by near infrared light or infrared light is outputted, and when the infrared cut filter is extracted, an image to which the light intensities of visible light and near infrared light are added is outputted.
An image to which near infrared light is added is suitable for object recognition although it is low in color reproducibility, and by combining a mechanism capable of obtaining this image and a mechanism emitting infrared light invisible to the human eye, a surveillance camera is realized with which clear images are obtained even at night. In the surveillance camera, the infrared cut filter is extracted from the incident optical path during the daytime.
A color correcting circuit is known that improves color reproducibility in the taken image without using the infrared cut filter when near infrared light is incident (see, for example, JP-A-2005-354457).
According to the technology described in JP-A-2005-354457, spectral sensitivity correcting means provided in a processing circuit changes the spectral sensitivity characteristic of the imaging signal to perform IR component separation, obtains the difference between the preceding and succeeding signals, and adds it up, thereby extracting the IR component. Since color reproducibility is degraded merely with the removal of the IR component, to improve color reproducibility, the spectral sensitivity correcting means matches the color data of each of red (R), green (G), and blue (B) having undergone the IR separation with the color balance of the target (for example, the color matching function of a person of normal color vision) by a matrix computation. To find the similarity between the current color and the target, the last squares method or the like is used.
With respect to the color arrangement of the color filter, an image sensing device of a four-color arrangement is known in which a repetition unit of the color arrangement is constituted by pixels of four, colors (see, for example, JP-A-2005-006066).
JP-A-2005-006066 discloses a color filter whose minimum repetition unit (pixel unit) is constituted by three primary color transmitting filters of red (R), green (G), and blue (B) and an infrared transmitting filter having sensitivity in the infrared light region and transmitting infrared light. JP-A-2005-006066 also describes that the infrared transmitting filter may be a filter of white (W).